It is well known to vacuum package perishable food as well as certain other products in order to exclude oxygen, moisture, dust and various forms of contamination. One reason for vacuum packaging is that in the case of a perishable food product, such product will degrade quickly in the presence of oxygen, so by removing air during the packaging of the product, its shelf life can be greatly increased.
Another reason for vacuum packaging is that an evacuated package containing a compressible product will displace a smaller volume than a non-evacuated package, thus enabling more economical shipping and storage costs.
After the food, the precision instruments, or the other item to be protected has been placed in a bag or package, some patentees have taught the placement of such packages in a vacuum chamber in order to withdraw the air through a vent in the package. After air removal, the vent is sealed. Examples of this particular technology are the Woods U.S. Pat. No. 3,545,983, entitled "Method of Deoxygenating and Packaging of Food Products," which issued Dec. 8, 1970, and the Waldrop et al U.S. Pat. No. 3,851,437, entitled "Receptacle Evacuation Apparatus and Method," which issued Dec. 3, 1974.
In pursuing techniques of this type, the oxygen content in food packages, for example, may be is reduced down to 11/2 percent or less by initially stripping a portion of the oxygen by exposing the food to flowing inert gas before it is placed in the packages. After this, the packages are placed in a vacuum chamber, and the oxygen-containing atmosphere is withdrawn, so as to cause fluid flow from each of the packages. When the chamber reaches a certain level of vacuum, dictated by the desired package hardness, the package may be hermetically sealed by sealing jaws in the chamber. Other techniques for sealing the packages are of course available.
In packaging by utilizing techniques of this type, it is known to place the packages in shaping devices, so that the completed packages will have a certain desired contour . Inasmuch as the contents of some packages initially contain air at atmospheric pressure, it is important to place such packages in devices preventing the expansion and subsequent bursting of the package when placed inside the vacuum chamber, as the pressure in the chamber is lowered.
Other patentees have taken a different route, with the King U.S. Pat. No. 3,216,832 entitled "Suction Packaging Method" involving an improvement upon the use of packaging constituted by lower and upper films of stretch wrap material. The items to be packaged are placed on the lower film, after which the air is withdrawn from the package. Such packages are sealed together peripherally after the air has been withdrawn, so as to draw the film into snug engagement with the product. In this particular patent to King, the patentee taught a preshaping of the bottom film to the product, so that there is less space to be evacuated, so that the film is drawn more readily into contact with the product, and so that less residual air is enclosed.
A somewhat different packaging technique involves a flexible package in which the product is placed, with a probe being inserted into the package through an open end of the package. The end of the package closes around the probe, after which the gases are removed from the package through the probe. Subsequently the probe is removed, and the package heat sealed.
My U.S. Pat. No. 4,534,152 entitled "Self Sealing Vacuumed Package," which issued Aug. 13, 1985 represented an advance in the art by teaching a method for the vacuum packaging of heat sensitive powdered products, perishable cheese products, and the like. Such product is placed in a thermoplastic bag, in the end of which I utilize a tortuous vent passage. The package is then placed in a supportive container having a two section cover, through which the tortuous vent passage protrudes. In this way, the bag is prevented from expanding and bursting when subjected to a vacuum.
The supportive container is then placed in a vacuum chamber such that the air inside the package is withdrawn through the vent passage. The vent passage collapses at such time as the vacuum chamber has been opened to atmospheric pressure, with such collapse of the vent passage forming a temporary seal, thus giving ample time for the package to thereafter be permanently sealed.
It was in an effort to improve still further upon these techniques that the present invention was evolved, which makes possible the use of a vacuum dome in achieving the vacuum packaging of a product, thus making the employment of a vacuum chamber unnecessary in many instances.